A grease composition comprising a lubricant oil and, as a thickening agent, fine powder of silica gel, aluminum hydroxide or ferric hydroxide dispersed in the oil is commercially available. Since the grease composition had such poor chemical resistance, it cannot be used as a grease for cocks of chemical equipment which contacts a corrosive gas such as CF.sub.3 Br, Br.sub.2, Cl.sub.2, F.sub.2, HF and ClF.sub.3. In addition, since its heat resistance is poor, it cannot be used in a high temperature environment.
To overcome these defects a grease composition comprising a low molecular weight polymer of trifluorochloroethylene, polyether having branched perfluoroalkyl groups and a fluororesin was proposed (cf. Japanese Patent Publication Nos. 18079/1964 and 45715/1974). Although the proposed grease composition has better chemical and heat resistance than the above describe it still had drawbacks such as the fluorine-containing base oil has high vapor pressure and tends to vaporize at a high temperature or in vacuo so that its application is limited.